One known technology for increasing a communication bandwidth using a plurality of lines is link aggregation, which is standardized in IEEE (The Institute of Electrical and Electronics Engineers, Inc.) 802.3ad. According to the link aggregation, frames are distributed to a plurality of lines based on MAC (Media Access Control) addresses, IP (Internet Protocol) addresses, or the like.
Besides, PTL 1 describes a method for transmitting data packets in parallel using a plurality of wireless channels or the like, and retransmitting them in case of failure in normal transmission. According to the method described in PTL 1, data frames accumulated in a transmission buffer are used to generate a plurality of data packets, each of which needs an identical transmission time, in units of packets that can be transmitted in parallel, and the data packets are transmitted consecutively in units of packets that can be transmitted in parallel. Then, if a plurality of data packets generated at a time need different transmission times, a dummy bit is added before parallel transmission to a data packet that needs a shorter transmission time so that all the data packets are transmitted in an identical time.